(1) Field of the Invention
This invention relates to thermosetting inorganic clay nanodispersions comprising an inorganic clay and at least one organometallic compound. The thermosetting inorganic clay nanodispersions are used to prepare thermosetting articles.
(2) Description of the Related Art
A composite is a solid material that results when two or more different materials having their own unique characteristics are combined to create a new material, and the combined properties, for the intended use, are superior to those of the separate starting materials. Typically, the composite is formed by embedding a fibrous material, e.g. glass fibers, into a polymer matrix. While the mechanical properties of a bundle of fibers are low, the strength of the individual fibers is reinforced by the polymer matrix that acts as an adhesive and binds the fibers together. The bound fibers provide rigidity and impart structural strength to the composite, while the polymeric matrix prevents the fibers from separating when the composite is subjected to environmental stress.
The polymeric matrix of the composite is formed from a thermoplastic or thermosetting resin, which is mixed with fibers used to make a composite. Thermoplastic polymers “soften” when heated, and recover their plastic properties when cooled. This reversible process can often be repeated many times. The polymers are thermoplastic because they are not chemically cross-linked. Examples of thermoplastic resins include linear polyethylene, polystyrene, acrylic resins, and nylon.
Thermosetting polymers “set” irreversibly by a curing reaction, and do not soften or melt when heated. The reason they do not soften or melt when they are heated is that they chemically cross-link when they are cured. Examples of thermosetting resins include phenolic resins, unsaturated polyester resins, polyurethane-forming resins, and epoxy resins.
Nanocomposites are composites which are formed by binding materials in the polymeric matrix that have a nanometer size range. Typically, the materials used to form nanocomposites are modified inorganic clays. Thermoplastic molded nanocomposite articles are particularly useful because they have improved mechanical properties, e.g. tensile strength (psi), modulus (ksi), elongation (%), and heat distortion temperature (° C.), when compared to conventional thermoplastic molded composite articles, which are not useful for some applications, e.g. elevated temperature use. Although conventional thermosetting molded composite articles have good mechanical properties, frequently they require improved performance properties.
Typical inorganic clays used in preparing nanocomposites include phyllosilicates such as montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite, magadiite, and kenyaite; vermiculite; and the like. Inorganic clays are typically multi-layered structures where the layers are close in proximity and contain cations of alkali metals or alkaline earth metals, e.g. sodium, potassium, or calcium, between the layers of the inorganic clay. The distance between the layers of the clay is the so-called “d-spacing”. Conventionally, in order to prepare nanocomposites from the inorganic clay, the inorganic clay, which is hydrophilic, is treated with water to “swell” the inorganic clay and thereby expand the d-spacing between the layers of the inorganic clay. The swollen clay is then treated with an intercalation agent, e.g. a quaternary ammonium salt, to render the inorganic clay organophilic (i.e. make the inorganic clay compatible with thermoplastic or thermosetting monomers and/or resins) and further increase the d-spacing by exchanging the cations of the inorganic clay with the cations of the intercalation agent. The intercalated inorganic clay is then recovered and dried. The treatment process is cumbersome and adds considerably to the cost of producing intercalated inorganic clays. The dried intercalated inorganic clay is then mixed with a thermoplastic polymer or thermosetting monomer or resin, which exfoliates (separates) some or all of the layers of the inorganic clay. In the case of thermoset resins, the mixture is cured by contacting with a curative and/or curing catalyst.
In order to form an article from the exfoliated inorganic clay, a filler is typically mixed with the exfoliated inorganic clay. Examples of fillers are silicas, talc, calcium carbonate, and aluminas. This mixture is then shaped by introducing it into a pattern. Thermoplastic mixtures are injected into the pattern in a molten state at elevated temperatures and form a nanocomposite article upon cooling. Thermosetting mixtures are introduced into the pattern in a liquid or flowable state, then cured (crosslinked) with a curative and/or curing catalyst to produce a shaped nanocomposite article.
As was mentioned previously, typically nanocomposite articles have good mechanical properties. However, if thermosetting nanocomposite articles could be produced with superior properties, these articles could replace conventional thermoset composite articles, e.g. sheet molding compounds (SMC).
All citations referred to under this description of the “Related Art” and in the “Detailed Description of the Invention” are expressly incorporated by reference.